Official Explanation
This is an assumption question. The conclusion and the premise are:
Premise: Businesses caught putting trash in public bins will be fined $250.
Conclusion: The new law will relieve the city’s overworked sanitation department.
In order for this law to truly reduce the work done by the sanitation department, you must assume that the fine or the threat of the fine will be sufficient to stop businesses from putting trash in the bins. If that assumption isn’t true, then the argument falls apart. Choice C states this assumption.
Choice A is not part of the argument, which deals with the businesses’ actions, not the public’s.
Choice B adds new information that is not part of the argument so eliminate it. It does not matter if cleaning out the public bins is the department’s most important job, so choice D is irrelevant.
Choice E also adds new information that isn’t necessary to the argument.
Answer: C.